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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Effect of 670-nm Light-Emitting Diode Light On Neuronal Cultures

Light close to and within the near infrared range has documented benefits for promoting wound healing in human and animal studies. Our preliminary results using light-emitting diodes (LEDs) in this range have also demonstrated two-to five-fold increases in growth-phase-specific DNA synthesis in normal fibroblasts, muscle cells, osteoblasts, and mucosal epithelial cells in tissue cultures. However, the mechanisms of action of such light on cells are poorly understood. We hypothesized that the therapeutic effects of such light result from the stimulation of cellular events associated with increases in cytochrome oxidase activity. As a first step in testing our hypothesis, we subjected primary neuronal cultures to impulse blockade by tetrodotoxin (TTX), a voltage-dependent sodium channel blocker, and applied LED light at 670 nm to determine if it could partially or fully reverse the reduction of cytochrome oxidase activity by TTX. The wavelength and parameters were previously tested to be beneficial for wound healing.

Wong-Riley, Margaret T. T.↗
NASA NTRS2003

Constant Applied Force Stimulates Osteoblast Proliferation Via Matrix-Integrin-Signaling Pathways

Reduced weight-bearing caused by immobilization, bed-rest or microgravity leads to atrophy in mechanosensitive tissue such as muscle and bone. We hypothesize that bone tissue requires earth s gravity (1-g) for the maintenance of extracellular matrix, integrin, and kinase-mediated cell growth and survival pathways. We investigate the role of matrix-integrin signaling in bone cells using cell culture centrifugation to provide different levels of hypergravity mechanostimulation. The 10-50-g range we use also mimics physiological intermedullary pressure (1.2 - 5 kPa). 24 hours at 50-g increased primary rat osteoblast proliferation on collagen Type I and fibronectin, but not laminin or uncoated plastic. BrdU incorporation in primary osteoblasts over 24 h showed hypergravity increased the number of cells actively synthesizing DNA from about 60% at 1-g to over 90% at 25-g. Primary rat fibroblasts grown at 50-g (24 h) showed no proliferation increase, suggesting this is a tissue-specific phenomenon. These results suggest that the betal and alpha4 integrins may be involved. To further test this, we used osteocytic-like MLO-Y4 cells that showed increased proliferation at 1-g with stable expression of a betal integrin cytoplasmic tail and transmembrane domain construct. At 50-g, MLO-Y4/betal cells showed greater MAPK activation than MLO-Y4 vector controls, suggesting that betal integrin is involved in transducing mitogenic signals in response to hypergravity. Preliminary results also show that interfering with the alpha4 integrin in primary osteoblasts grown on fibronectin blocked the proliferation response. These results indicate that cells from mechanosensitive bone tissue can respond to gravity-generated forces, and this response involves specific matrix and integrin-dependent signaling pathways.

Vercoutere, W.↗
NASA NTRS2003

Hypergravity Stimulates Osteoblast Proliferation Via Matrix-Integrin-Signaling Pathways

Extensive characterizations of the physiologic consequences of microgravity and gravity indicate that lack of weight-bearing may cause tissue atrophy through cellular and subcellular level mechanisms. We hypothesize that gravity is needed for the efficient transduction of cell growth and survival signals from the extra-cellular matrix (ECM) in mechanosensitive tissues. Recent work from our laboratory and from others shows that an increase of gravity increases bone cell growth and survival. We found that 50-g hypergravity stimulation increased osteoblast proliferation for cells grown on Collagen Type I and Fibronectin, but not on Laminin or uncoated plastic. This may be a tissue-specific response, because 50-g hypergravity stimulation caused no increase in proliferation for primary rat fibroblasts. These results combined with RT-PCR for all possible integrins indicate that beta1 integrin subunit may be involved. The osteoblast proliferation response on Collagen Type I was greater at 25-g than at 10-g or 50-g; 24-h duration of hypergravity was necessary to see an increase in proliferation. Survival was enhanced during hypergravity stimulation by the presence of matrix. Flow cytometry analysis indicated that cell cycle may be altered; BrdU incorporation in proliferating cells showed an increase in the number of actively dividing cells from about 60% at 1-g to over 90% at 25-g. To further investigate the molecular components involved, we applied fluorescence labeling of cytoskeletal and signaling molecules to cells after 2 to 30 minutes of hypergravity stimulation. While structural components did not appear to be altered, phosphorylation increased, indicating that signaling pathways may be activated. These data indicate that gravity mechanostimulation of osteoblast proliferation involves specific matrix-integrin signaling pathways which are sensitive to duration and g-level.

Vercoutere, W.↗
NASA NTRS2003

The endomembrane requirement for cell surface repair

The capacity to reseal a plasma membrane disruption rapidly is required for cell survival in many physiological environments. Intracellular membrane (endomembrane) is thought to play a central role in the rapid resealing response. We here directly compare the resealing response of a cell that lacks endomembrane, the red blood cell, with that of several nucleated cells possessing an abundant endomembrane compartment. RBC membrane disruptions inflicted by a mode-locked Ti:sapphire laser, even those initially smaller than hemoglobin, failed to reseal rapidly. By contrast, much larger laser-induced disruptions made in sea urchin eggs, fibroblasts, and neurons exhibited rapid, Ca(2+)-dependent resealing. We conclude that rapid resealing is not mediated by simple physiochemical mechanisms; endomembrane is required.

NASA Discipline Cell Biology↗
NASA NTRS2003

Are chromosomal instabilities induced by exposure of cultured normal human cells to low- or high-LET radiation?

Radiation-induced genomic instability has been proposed as a very early, if not an initiating, step in radiation carcinogenesis. Numerous studies have established the occurrence of radiation-induced chromosomal instability in various cells of both human and rodent origin. In many of these studies, however, the cells were not "normal" initially, and in many cases they involved tumor-derived cell lines. The phenomenon clearly would be of even greater interest if it were shown to occur generally in cells that are normal at the outset, rather than cells that may have been "selected" because of a pre-existing susceptibility to induced instability. As a test of the generality of the phenomenon, we studied low-passage normal diploid human fibroblasts (AG1521A) to determine whether they are susceptible to the induction of chromosomal instability in the progeny of surviving cells after exposure in G(0) to low- and high-LET radiation. Cytogenetic assays for instability were performed on both mixed populations of cells and clones of cells surviving exposure. We found no evidence for the induction of such instability as a result of radiation exposure, though we observed a senescence-related chromosomal instability in the progeny of both irradiated and unirradiated cell populations. Copyright 2003 by Radiation Research Society.

Non-NASA Center↗
NASA NTRS2002

Silencing expression of the catalytic subunit of DNA-dependent protein kinase by small interfering RNA sensitizes human cells for radiation-induced chromosome damage, cell killing, and mutation

Targeted gene silencing in mammalian cells by RNA interference (RNAi) using small interfering RNAs (siRNAs) was recently described by Elbashir et al. (S. M. Elbashir et al., Nature (Lond.), 411: 494-498, 2001). We have used this methodology in several human cell strains to reduce expression of the Prkdc (DNA-PKcs) gene coding for the catalytic subunit of the DNA-dependent protein kinase (DNA-PKcs) that is involved in the nonhomologous end joining of DNA double-strand breaks. We have also demonstrated a radiosensitization for several phenotypic endpoints of radiation damage. In low-passage normal human fibroblasts, siRNA knock-down of DNA-PKcs resulted in a reduced capacity for restitution of radiation-induced interphase chromosome breaks as measured by premature chromosome condensation, an increased yield of acentric chromosome fragments at the first postirradiation mitosis, and an increased radiosensitivity for cell killing. For three strains of related human lymphoblasts, DNA-PKcs-targeted siRNA transfection resulted in little or no increase in radiosensitivity with respect to cell killing, a 1.5-fold decrease in induced mutant yield in TK6- and p53-null NH32 cells, but about a 2-fold increase in induced mutant yield in p53-mutant WTK1 cells at both the hypoxanthine quanine phosphoribosyl transferase (hprt) and the thymidine kinase loci.

Non-NASA Center↗
NASA NTRS2001

Evidence for factors modulating radiation-induced G2-delay: potential application as radioprotectors

Manipulation of checkpoint response to DNA damage can be developed as a means for protecting astronauts from the adverse effects of unexpected, or background exposures to ionizing radiation. To achieve this goal reagents need to be developed that protect cells from radiation injury by prolonging checkpoint response, thus promoting repair. We present evidence for a low molecular weight substance excreted by cells that dramatically increases the duration of the G2-delay. This compound is termed G2-Arrest Modulating Activity (GAMA). A rat cell line (A1-5) generated by transforming rat embryo fibroblasts with a temperature sensitive form of p53 plus H-ras demonstrates a dramatic increase in radiation resistance after exposure to low LET radiation that is not associated with an increase in the efficiency of rejoining of DNA double strand breaks. Radioresistance in this cell line correlates with a dramatic increase in the duration of the G2 arrest that is modulated by a GAMA produced by actively growing cells. The properties of GAMA suggest that it is a low molecular weight heat-stable peptide. Further characterization of this substance and elucidation of its mechanism of action may allow the development of a biological response modifier with potential applications as a radioprotector. GAMA may be useful for protecting astronauts from radiation injury as preliminary evidence suggests that it is able to modulate the response of cells exposed to heavy ion radiation, similar to that encountered in outer space.

NASA Discipline Radiation Health↗
NASA NTRS2001

Cyclic strain increases protease-activated receptor-1 expression in vascular smooth muscle cells

Cyclic strain regulates many vascular smooth muscle cell (VSMC) functions through changing gene expression. This study investigated the effects of cyclic strain on protease-activated receptor-1 (PAR-1) expression in VSMCs and the possible signaling pathways involved, on the basis of the hypothesis that cyclic strain would enhance PAR-1 expression, reflecting increased thrombin activity. Uniaxial cyclic strain (1 Hz, 20%) of cells cultured on elastic membranes induced a 2-fold increase in both PAR-1 mRNA and protein levels. Functional activity of PAR-1, as assessed by cell proliferation in response to thrombin, was also increased by cyclic strain. In addition, treatment of cells with antioxidants or an NADPH oxidase inhibitor blocked strain-induced PAR-1 expression. Preincubation of cells with protein kinase inhibitors (staurosporine or Ro 31-8220) enhanced strain-increased PAR-1 expression, whereas inhibitors of NO synthase, tyrosine kinase, and mitogen-activated protein kinases had no effect. Cyclic strain in the presence of basic fibroblast growth factor induced PAR-1 mRNA levels beyond the effect of cyclic strain alone, whereas no additive effect was observed between cyclic strain and platelet-derived growth factor-AB. Our findings that cyclic strain upregulates PAR-1 mRNA expression but that shear stress downregulates this gene in VSMCs provide an opportunity to elucidate signaling differences by which VSMCs respond to different mechanical forces.

NASA Discipline Cell Biology↗
NASA NTRS2001

Differential expression of neuroleukin in osseous tissues and its involvement in mineralization during osteoblast differentiation

Osteoblast differentiation is a multistep process that involves critical spatial and temporal regulation of cellular processes marked by the presence of a large number of differentially expressed molecules. To identify key functional molecules, we used differential messenger RNA (mRNA) display and compared RNA populations isolated from the defined transition phases (proliferation, matrix formation, and mineralization) of the MC3T3-E1 osteoblast-like cell line. Using this approach, a complementary DNA (cDNA) fragment was isolated and identified as neuroleukin (NLK), a multifunctional cytokine also known as autocrine motility factor (AMF), phosphoglucose isomerase (PGI; phosphohexose isomerase [PHI]), and maturation factor (MF). Northern analysis showed NLK temporal expression during MC3T3-E1 cell differentiation with a 3.5-fold increase during matrix formation and mineralization. Immunocytochemical studies revealed the presence of NLK in MC3T3-E1 cells as well as in the surrounding matrix, consistent with a secreted molecule. In contrast, the NLK receptor protein was detected primarily on the cell membrane. In subsequent studies, a high level of NLK expression was identified in osteoblasts and superficial articular chondrocytes in bone of 1-, 4-, and 8-month-old normal mice, as well as in fibroblasts, proliferating chondrocytes, and osteoblasts within a fracture callus. However, NLK was not evident in hypertrophic chondrocytes or osteocytes. In addition, treatment of MC3T3 cells with 6-phosphogluconic acid (6PGA; a NLK inhibitor) resulted in diminishing alkaline phosphatase (ALP) activity and mineralization in MC3T3-E1 cells, especially during the matrix formation stage of differentiating cells. Taken together, these data show specific expression of NLK in discrete populations of bone and cartilage cells and suggest a possible role for this secreted protein in bone development and regeneration.

NASA Discipline Musculoskeletal↗
NASA NTRS1995

Integrin-extracellular matrix interactions in connective tissue remodeling and osteoblast differentiation

The differentiaton of bone cells is a complex multistep process. Bone is somewhat unusual in that it is very actively and continually remodeled in the adult and that maintenance of its mass in the mature organism is exquisitely sensitive to mechanical as well as chemical signals. Bone is also unique because it consists of a very large amount of extracellular matrix (ECM) that is mineralized. The integrin family of ECM receptors has been shown to play an important role in tissue morphogenesis in several systems. Our studies on the regulation of matrix remodeling enzymes by integrins in rabbit synovial fibroblasts show that two b1 integrin fibronectin (FN) receptor complexes (alpha 5 beta 1 and alpha 4 beta 1) cooperate in detecting subtle changes in the composition of the ECM. As a result of signal transduction by these integrins, the levels of mRNA and protein for several members of the metalloproteinase family are regulated in these cells. We have also used antibody and RGD peptide perturbation studies to determine the significance of cell/ECM interactions to normal osteogenesis. We found that interactions between the cell binding domain of FN and integrins are required for both normal morphogenesis and gene expression in cultured osteoblasts that differentiate to form bone-like tissue in culture. These data lead us to propose that beta 1 integrins play an important role in osteoblast differentiation as well as in bone remodeling.

NASA Discipline Number 26-10↗
NASA NTRS1992

The role of a cell surface inhibitor in early signal transduction associated with the regulation of cell division and differentiation

Serum stimulation of quiescent human fibroblast cultures resulted in a hyperphosphorylation of the nuclear retinoblastoma gene susceptibility product (RB). However, serum stimulation in the presence of 9 x 10(-8) M of a purified bovine sialoglycopeptide (SGP) cell surface inhibitor abrogated the hyperphosphorylation of the RB protein and the subsequent progression of cells through the mitotic cycle. The experimental results suggest that the SGP mediated its cell cycle arrest at a site in the cell cycle that was at the time of RB phosphorylation or somewhat upstream of the modification of this regulatory protein of cell division. Both cells serum-deprived and serum stimulated in the presence of the SGP displayed only a hypophosphorylated RB protein, consistent with the SGP-mediated cell cycle arrest point being near the G1/S interface.

NASA Discipline Cell Biology↗
NASA NTRS1993

The use of the tyrosine phosphatase antagonist orthovanadate in the study of a cell proliferation inhibitor

Incubation of murine fibroblasts with orthovanadate, a global tyrosine phosphatase inhibitor, was shown to confer a "pseudo-transformed" phenotype with regard to cell morphology and growth characteristics. This alteration was manifested by both an increasing refractile appearance of the cells, consistent with many transformed cell lines, as well as an increase in maximum cell density was attained. Despite the abrogation of cellular tyrosine phosphatase activity, orthovanadate-treated cells remained sensitive to the biological activity of a naturally occurring sialoglycopeptide (SGP) cell surface proliferation inhibitor. The results indicated that tyrosine phosphatase activity, inhibited by orthovanadate, was not involved in the signal transduction pathway of the SGP.

NASA Discipline Number 93-10↗
NASA NTRS2003

Multilineage differentiation of rhesus monkey embryonic stem cells in three-dimensional culture systems

In the course of normal embryogenesis, embryonic stem (ES) cells differentiate along different lineages in the context of complex three-dimensional (3D) tissue structures. In order to study this phenomenon in vitro under controlled conditions, 3D culture systems are necessary. Here, we studied in vitro differentiation of rhesus monkey ES cells in 3D collagen matrixes (collagen gels and porous collagen sponges). Differentiation of ES cells in these 3D systems was different from that in monolayers. ES cells differentiated in collagen matrixes into neural, epithelial, and endothelial lineages. The abilities of ES cells to form various structures in two chemically similar but topologically different matrixes were different. In particular, in collagen gels ES cells formed gland-like circular structures, whereas in collagen sponges ES cells were scattered through the matrix or formed aggregates. Soluble factors produced by feeder cells or added to the culture medium facilitated ES cell differentiation into particular lineages. Coculture with fibroblasts in collagen gel facilitated ES cell differentiation into cells of a neural lineage expressing nestin, neural cell adhesion molecule, and class III beta-tubulin. In collagen sponges, keratinocytes facilitated ES cell differentiation into cells of an endothelial lineage expressing factor VIII. Exogenous granulocyte-macrophage colony-stimulating factor further enhanced endothelial differentiation. Thus, both soluble factors and the type of extracellular matrix seem to be critical in directing differentiation of ES cells and the formation of tissue-like structures. Three-dimensional culture systems are a valuable tool for studying the mechanisms of these phenomena.

Pluripotent Stem Cells/cytology/physiology↗
NASA NTRS2001

The radioresistance to killing of A1-5 cells derives from activation of the Chk1 pathway

Checkpoints respond to DNA damage by arresting the cell cycle to provide time for facilitating repair. In mammalian cells, the G(2) checkpoint prevents the Cdc25C phosphatase from removing inhibitory phosphate groups from the mitosis-promoting kinase Cdc2. Both Chk1 and Chk2, the checkpoint kinases, can phosphorylate Cdc25C and inactivate its in vitro phosphatase activity. Therefore, both Chk1 and Chk2 are thought to regulate the activation of the G(2) checkpoint. Here we report that A1-5, a transformed rat embryo fibroblast cell line, shows much more radioresistance associated with a much stronger G(2) arrest response when compared with its counterpart, B4, although A1-5 and B4 cells have a similar capacity for nonhomologous end-joining DNA repair. These phenotypes of A1-5 cells are accompanied by a higher Chk1 expression and a higher phosphorylation of Cdc2. On the other hand, Chk2 expression increases slightly following radiation; however, it has no difference between A1-5 and B4 cells. Caffeine or UCN-01 abolishes the extreme radioresistance with the strong G(2) arrest and at the same time reduces the phosphorylation of Cdc2 in A1-5 cells. In addition, Chk1 but not Chk2 antisense oligonucleotide sensitizes A1-5 cells to radiation-induced killing and reduces the G(2) arrest of the cells. Taken together these results suggest that the Chk1/Cdc25C/Cdc2 pathway is the major player for the radioresistance with G(2) arrest in A1-5 cells.

NASA Discipline Radiation Health↗
NASA NTRS2001

Relative effectiveness of HZE iron-56 particles for the induction of cytogenetic damage in vivo

One of the risks of prolonged manned space flight is the exposure of astronauts to radiation from galactic cosmic rays, which contain heavy ions such as (56)Fe. To study the effects of such exposures, experiments were conducted at the Brookhaven National Laboratory by exposing Wistar rats to high-mass, high-Z, high-energy (HZE) particles using the Alternating Gradient Synchrotron (AGS). The biological effectiveness of (56)Fe ions (1000 MeV/nucleon) relative to low-LET gamma rays and high-LET alpha particles for the induction of chromosome damage and micronuclei was determined. The mitotic index and the frequency of chromosome aberrations were evaluated in bone marrow cells, and the frequency of micronuclei was measured in cells isolated from the trachea and the deep lung. A marked delay in the entry of cells into mitosis was induced in the bone marrow cells that decreased as a function of time after the exposure. The frequencies of chromatid aberrations and micronuclei increased as linear functions of dose. The frequency of chromosome aberrations induced by HZE particles was about 3.2 times higher than that observed after exposure to (60)Co gamma rays. The frequency of micronuclei in rat lung fibroblasts, lung epithelial cells, and tracheal epithelial cells increased linearly, with slopes of 7 x 10(-4), 12 x 10(-4), and 11 x 10(-4) micronuclei/binucleated cell cGy(-1), respectively. When genetic damage induced by radiation from (56)Fe ions was compared to that from exposure to (60)Co gamma rays, (56)Fe-ion radiation was between 0.9 and 3.3 times more effective than (60)Co gamma rays. However, the HZE-particle exposures were only 10-20% as effective as radon in producing micronuclei in either deep lung or tracheal epithelial cells. Using microdosimetric techniques, we estimated that 32 cells were hit by delta rays for each cell that was traversed by the primary HZE (56)Fe particle. These calculations and the observed low relative effectiveness of the exposure to HZE particles suggest that at least part of the cytogenetic damage measured was caused by the delta rays. Much of the energy deposited by the primary HZE particles may result in cell killing and may therefore be "wasted" as far as production of detectable micronuclei is concerned. The role of wasted energy in studies of cancer induction may be important in risk estimates for exposure to HZE particles.

Non-NASA Center↗
NASA NTRS2000

Homologous recombination as a potential target for caffeine radiosensitization in mammalian cells: reduced caffeine radiosensitization in XRCC2 and XRCC3 mutants

The radiosensitizing effect of caffeine has been associated with the disruption of multiple DNA damage-responsive cell cycle checkpoints, but several lines of evidence also implicate inhibition of DNA repair. The role of DNA repair inhibition in caffeine radiosensitization remains uncharacterized, and it is unknown which repair process, or lesion, is affected. We show that a radiosensitive cell line, mutant for the RAD51 homolog XRCC2 and defective in homologous recombination repair (HRR), displays significantly diminished caffeine radiosensitization that can be restored by expression of XRCC2. Despite the reduced radiosensitization, caffeine effectively abrogates checkpoints in S and G2 phases in XRCC2 mutant cells indicating that checkpoint abrogation is not sufficient for radiosensitization. Another radiosensitive line, mutant for XRCC3 and defective in HRR, similarly shows reduced caffeine radiosensitization. On the other hand, a radiosensitive mutant (irs-20) of DNA-PKcs with a defect in non-homologous end-joining (NHEJ) is radiosensitized by caffeine to an extent comparable to wild-type cells. In addition, rejoining of radiation-induced DNA DSBs, that mainly reflects NHEJ, remains unaffected by caffeine in XRCC2 and XRCC3 mutants, or their wild-type counterparts. These observations suggest that caffeine targets steps in HRR but not in NHEJ and that abrogation of checkpoint response is not sufficient to explain radiosensitization. Indeed, immortalized fibroblasts from AT patients show caffeine radiosensitization despite the checkpoint defects associated with ATM mutation. We propose that caffeine radiosensitization is mediated by inhibition of stages in DNA DSB repair requiring HRR and that checkpoint disruption contributes by allowing these DSBs to transit into irreparable states. Thus, checkpoints may contribute to genomic stability by promoting error-free HRR.

NASA Discipline Radiation Health↗
NASA NTRS2000

IR spectroscopic characteristics of cell cycle and cell death probed by synchrotron radiation based Fourier transform IR spectromicroscopy

Synchrotron radiation based Fourier transform IR (SR-FTIR) spectromicroscopy allows the study of individual living cells with a high signal to noise ratio. Here we report the use of the SR-FTIR technique to investigate changes in IR spectral features from individual human lung fibroblast (IMR-90) cells in vitro at different points in their cell cycle. Clear changes are observed in the spectral regions corresponding to proteins, DNA, and RNA as a cell changes from the G(1)-phase to the S-phase and finally into mitosis. These spectral changes include markers for the changing secondary structure of proteins in the cell, as well as variations in DNA/RNA content and packing as the cell cycle progresses. We also observe spectral features that indicate that occasional cells are undergoing various steps in the process of cell death. The dying or dead cell has a shift in the protein amide I and II bands corresponding to changing protein morphologies, and a significant increase in the intensity of an ester carbonyl C===O peak at 1743 cm(-1) is observed. Copyright John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 57: 329-335, 2000.

Non-NASA Center↗
NASA NTRS2000

Cardiac tissue enriched factors serum response factor and GATA-4 are mutual coregulators

Combinatorial interaction among cardiac tissue-restricted enriched transcription factors may facilitate the expression of cardiac tissue-restricted genes. Here we show that the MADS box factor serum response factor (SRF) cooperates with the zinc finger protein GATA-4 to synergistically activate numerous myogenic and nonmyogenic serum response element (SRE)-dependent promoters in CV1 fibroblasts. In the absence of GATA binding sites, synergistic activation depends on binding of SRF to the proximal CArG box sequence in the cardiac and skeletal alpha-actin promoter. GATA-4's C-terminal activation domain is obligatory for synergistic coactivation with SRF, and its N-terminal domain and first zinc finger are inhibitory. SRF and GATA-4 physically associate both in vivo and in vitro through their MADS box and the second zinc finger domains as determined by protein A pullout assays and by in vivo one-hybrid transfection assays using Gal4 fusion proteins. Other cardiovascular tissue-restricted GATA factors, such as GATA-5 and GATA-6, were equivalent to GATA-4 in coactivating SRE-dependent targets. Thus, interaction between the MADS box and C4 zinc finger proteins, a novel regulatory paradigm, mediates activation of SRF-dependent gene expression.

NASA Discipline Musculoskeletal↗